After a hydrocarbon well has been drilled and made safe, a well testing operation is generally carried out for a short period of time. The well testing operation serves to characterize the various components of the well, and to estimate the production capacities of the well. An aspect of the test is to separate certain phases of the effluent, typically water, oil, and gas. Since the various phases are of different densities, separation takes place continuously in a gravity separator, in which the phases settle out. The gravity separator can be a vertical or a horizontal separator.
FIG. 1 shows a hydrocarbon well OW and a well testing arrangement. An effluent E flows out of the well from a well head WH. The well head WH is connected to a well testing arrangement. The well testing arrangement typically comprises a chain of elements connected together, namely a pressure reducer PR, a heat exchanger HE and a separator S. The hydrocarbons that have been separated are burnt off: oil is burnt in an oil burner OD and gas is flared in a gas flare GD. The separated aqueous phase is discharged WD, optionally after undergoing additional purification.
At the beginning of the well testing operation—the clean-up period—the composition of the effluent varies considerably. The well is initially filled with aqueous residues from the well construction operation such as drilling fluid and completion fluid. The effluent that is initially collected is essentially made up of water. During the clean up period, the percentage of aqueous residue decreases gradually, and the composition of the effluent becomes enriched with oil and with gas.
A separator can be sized such as to treat an effluent whose phase fractions remain substantially stable over time. Such a separator is not well adapted to handle an effluent with substantially varying phase fractions as encountered at the beginning of the clean-up period. A first solution consists in sending the effluent directly to the burner. This solution results in un-burnt hydrocarbons and an environmental pollution problem. A second solution consists in storing effluent in containers, waiting long enough for gravity separation and subsequent disposal of the different phase. A third solution consists in building an effluent treatment installation near the well. The last two solutions result in costly and voluminous equipment.
WO 0183073 describes a separator comprising an adjustment arrangement for adjusting the geometrical separation characteristics of the separator in dependence on the different phase fractions in the effluent.
A first exemplary embodiment of the adjustment arrangement consists in a weir plate assembly of variable height, e.g. under the form of telescopic plates.
A second exemplary embodiment of the adjustment arrangement consists in a duct assembly of variable height, e.g. under the form of telescopic tube or bellows comprising a recovery duct terminated by a suction intake.
Both embodiments are actuated by a mechanical actuator (pneumatic, hydraulic, electrical or lever arm).
This arrangement combined with a regulation of the flow-rate of the different phases flowing in and out of the separator enable an efficient and pollution free treatment of variable phase ratio effluent.